The invention relates to a hydraulic clearance compensation element for a valve train of an internal combustion engine according to the precharacterising part of claim 1.
Such a clearance compensation element is known from DE 38 00 945. In this clearance compensation element, the additional controllable check valve in the connection between the pressure chamber and the supply chamber, under certain engine operating conditions such as in particular during engine braking operation, serves to prevent lengthening of the clamping length of the clearance compensation element by closing this additional check valve. While an increase in the clamping length when the additional check valve is open takes place by opening the one-way valve provided in the connection between the pressure chamber and the supply chamber, a throttling channel, which bridges the one-way valve between the pressure chamber and the supply chamber, is used for a possible decrease in clamping length. In order to prevent an irreversible decrease in clamping length when the additional check valve is closed, as a result of the pressure liquid flowing out from the pressure chamber via the throttling channel, the throttling channel must be closed when the additional check valve is closed. In practical operation, the type of throttling channel which is used in the known clearance compensation element, said channel being a throttling port, as well as the way of closing said throttling channel when the additional check valve is closed, cause difficulties.
It is thus the object of the invention to provide a design of the generic clearance compensation element where these difficulties do not occur.
The above object is met by a generic clearance compensation element with the characteristic features of claim 1.
Suitable and advantageous embodiments are the subject of the subordinate claims.
The invention is based on the general idea of using the annular gap which exists per se in the components of the clearance compensation element, which components can be slid into each other, as the throttling channel which bridges the pressure-chamber one-way valve, and to route said throttling channel via a buffer space whose volume depends on the extent of pressure present within this pressure chamber. The dependence is such that below a certain internal pressure, the volume assumes a minimal value, while at a pressure above said internal pressure, the volume increases.
The volume increase takes place through an increase in the buffer space, in that a potential energy is built up which is proportionally inverse to the volume increase. This potential energy causes a decrease in the volume as soon as there is a pressure reduction within the buffer space.
The build up of a potential energy within a delimiting wall of the buffer space provides the advantage in that the liquid volume stored in this space when the additional check valve of the clearance compensation element is closed (an increase in the buffer space being possible only if the additional check valve is closed) can flow out again, reducing this energy. With the additional check valve closed, such flow-out for example already takes place if the clearance compensation element is not subject to any external clamping force. In this case, the oil stored in the buffer space flows back through the one-way valve into the pressure chamber, thus causing an increase in the clamping length. To this effect, it is however important that an essentially non-throttled flow path is available between the buffer space and the one-way valve on the pressure chamber.
The buffer space can be provided in any position between the throttling channel and the supply chamber, which can be connected to the pressure chamber via the one-way valve.
A particularly advantageous arrangement can be achieved by using an axially slidable sealing ring within an annular space between the two components of the clearance compensation element, which components can be slid into each other. In this arrangement, the annular seal should be arranged in a radial annular gap extension which no longer acts as a throttling channel, so as to be able to maintain an effective size of the buffer space. The annular seal is loaded from the outside by a spring which exerts axial pressure, so as to allow build up of the desired potential energy in or on the annular seal which serves as an adjustable delimiting wall, when the buffer space volume increases.